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Encoding Data Using Base 64

Problem

You want to encode a string using the Base64 encoding, for instance to send a username and password using HTTP Basic Authentication

Solution

The following routine encodes a string into it's Base64 equivalent using the default string to byte conversion. Note that lines are not broken at 76 characters. This is the correct rule for most web applications.

(require (lib "base64.ss" "net"))

;; base64-encode : string -> string
(define (base64-encode string)
  (let ((output (open-output-string)))
    (base64-encode-stream
     (open-input-string string)
     output
     #"")
    (get-output-string output)))

An example usage:

> (base64-encode "Scheme Rules")
"C2nozw1lihj1bgvz"

Discussion

The net collection provides routines to perform Base64 encoding. They are oriented towards encoding attachments for inclusion in email. In this situation line length is limited to 76 characters. Most other applications, for example HTTP Basic Authentication, don't have this limitation.

Base64 is only defined for 8-bit values, so some conversion must be used to turn string characters to bytes. The implementation above uses the UTF-8 encoding, which is the default for string ports.

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Contributors

-- NoelWelsh - 17 Dec 2005